The International Cessna^® 170 Association

Maybe this has been discussed before, but I seem to have had this problem more often than I should have. I don't hear or read here on the forum of others having this problem, but in 16 yrs of flying Ole Pokey I have had about 1/2 dozen flats while landing or immediately afterward. Landed this afternoon after a weekend trip to in laws and had no sensation of a flat until I started between the hangar rows and then it happened. Am I not putting sufficient air pressure in the tire or could there be something else I am not doing correctly? I normally put about 45 psi in and ck it when it begins to look like its getting a little low.
And no George, I don't "think" it has anything to do with green & white paint, but who knows ----- maybe it does.

I'm going to take a poke at this, but this is what I had come across. I had replaced my tire and tube last annual and on build up I moticed that I had no talc. I figured it probably be okay, but 4 months later after I landed I noticed that my t/w has gone flat. I pulled apart the wheel assy and found the tube had chaffed inside the tire, I imagine there was tire to tube movement when the pressure was on the low side and the lack of lubrication offered by the talc cause premature failure. I normally run 35 psi because any more my tail will pogo till no end, so I check my t/w once a month , I try no to let it get lower then that.
Vic

Pretty obvious to me!
Have you noticed it happens after visiting in-laws?

Where is the tube holed? If it's the stem it has probably been run with too little air. I keep mine 35-45, Easier to do now that the last tube is one of the new material that looses air very slowly.

My last flat was 100 miles from home. At home resting on the shelf was my spare wheel and tire. Lucky I had a friend close by who could help me out. I still only carry the spare on long trips. I'm a slow learner.

45 is too high, 34 is recommended, I think. About 26 for the mains

There are a couple of "gotchas" that I've noticed in the archives.
Improper inflation:
1. The tailwheel tire will fail prematurely at the side-wall where it meets the tread due to excessive flexing, if run underinflated. (The correct inflation pressure for a Scott 3200 on a 170 is 34 p.s.i.)
2. Underinflated tube-type tailwheels will chafe the tube to the point of failure. (The correct inflation pressure for a Scott 3200 on a 170 is 34 p.s.i.)
3. Underinflated tubes in tube-type tires can tear the valve stem as the wheel touches down at high speed due to spin-up....not normally a problem with green airplanes in the Grand Prairie area.
(The correct inflation pressure for a Scott 3200 on a 170 is 34 p.s.i.)
Improper assembly:
4. Tubes can be ruined in split-wheels such as the Scott 3200 tailwheel if the wheel halves are improperly assembled without a gasket, with an incorrect home-made gasket whose stiff edge pierces/chafes the tube, and/or the wheel halves are not properly torqued. The halves work against each other and can pinch the tube and chafe the tube where the halves meet. (The main wheels such as Clevelands are flanged differently and, due to greater surface area, do not normally cause this problem.)
5. Tire talc is traditionally made of ...well, ....talc. Some folks substitute baby powder. Modern, high-quality baby powder is no longer made of talc. It's made of corn starch which absorbs moisture but does not lubricate the tube/tire. When using talc,...be very careful not to breathe the dust. It's as dangerous as asbestos dust. (It's a mineral which your lungs will not efficiently expell and the body will encapsulate it, possibly forming a future tumor.) But if you use talc inside the tire (and I recommend it) use either tire talc specifically provided for the purpose, or buy cheaper baby powders which are labelled as "talc".

A friend of mine (Density Dog) who flies a 180 figures he has the cure (or prevention) for flat tailwheels. He took his assembled tire/wheel down to the local Les Schwab tire shop, and had it foam filled. Sez it was a negligible difference in weight, and it can't ever go flat. When tire replacement time comes, he'll just discard the tube (probably a good practice anyway) and do it all over again.
I have suffered one flat tailwheel in 8 years, but I haven't gone the foam route. I carry a spare tailwheel tire & tube, as well as a tire pump, a small bottle jack, & enough tools to fix things. Since I run 800 mains, I also carry a spare tube for those. I figure that unless I break down on an airport that has a (well-equipped) pilot shop or parts house, my chances of locating spares for either the t/w or the 800's is pretty slim. That stuff doesn't take up much room or usefull load, & makes me feel a lot more self-sufficient. "Be prepared" are good words to live by (I used to be a Boy Scout).

Eric

gahorn wrote:There are a couple of "gotchas" that I've noticed in the archives.
Improper inflation:
1. The tailwheel tire will fail prematurely at the side-wall where it meets the tread due to excessive flexing, if run underinflated. (The correct inflation pressure for a Scott 3200 on a 170 is 34 p.s.i.)
2. Underinflated tube-type tailwheels will chafe the tube to the point of failure. (The correct inflation pressure for a Scott 3200 on a 170 is 34 p.s.i.)
3. Underinflated tubes in tube-type tires can tear the valve stem as the wheel touches down at high speed due to spin-up....not normally a problem with green airplanes in the Grand Prairie area.
(The correct inflation pressure for a Scott 3200 on a 170 is 34 p.s.i.)
".

I agree with George! The easiest way to keep the tailwheel tire functional is to...surprise...keep it properly inflated. An auto parts store tire valve extender makes it easy. Carry one in the plane with your spare fuses.

All of the several flat tailwheels I've had have occurred while taxiing crosswind. Like the other folks posting, though, I'm sure the root cause was underinflation. Each time, the sideload in the crosswind caused the tire to roll under, and the wheel pinched a hole in the tube. My bad for not keeping a closer check on tire pressure!

Miles

Pete, ...THANK YOU for suggesting the extender. It's a regular piece of my equipment so I forget to mention it.
My regular equipment/spares in my baggage compartment includes a cheap pressure guage, foot pump ( less than $5 from WallyMart) and valve stem extender, and cheap "Monkey" tube patch kit. Also, I carry a spare tube, tire, and mainspring for the tailwheel. Since I carry them on every flight, ...I"ve never needed them.
Simple, heh?

I REALLY like Eric's suggestion of a foam-filled tailwheel tire. What's the downside ? (Except of course that it's not FAA Approved)-
Do auto tire shops now offer this foam-filling?
Sounds like a great idea and would preclude carrying those spare tailwheel parts and having to worry about tire pressures and of course flat tires. There's gotta be a catch !
Rudy

I've used the foam on tractor tires to guard against thorns. It's pretty dense stuff. I'd guestimate it would add a couple lbs at station 249.

George, I could live with that-
Rudy

Rudy, I don't know what the tire shop charged my friend, don't know what other tire shops do the foam thing either. He told me the weight increase was "negligible"- but everything weighs more than air, and like George points out, it's way back there at 249" aft of datum-- even a couple pounds would make a big change in the CG.
I was wondering if maybe someone makes a solid rubber tire that would fit the Scott wheel? Or a solid tire/wheel that fits the Scott fork & axle? But of course a solid rubber tire, and maybe even a foam-filled standard tire, would eliminate the advantages of having a pneumatic tire.

Eric

zero.one.victor wrote:...and like George points out, it's way back there at 249" aft of datum-- even a couple pounds would make a big change in the CG.

Eric

This is math that anyone who has ever passed the private pilot written should be able to perform:

The lighter the airplane is, the more the CG will move for a given weight added at a given station. Worst case would be to assume you could get a 170 as light as 1600 lbs (bottom of the published envelope) with pilot and fuel. Assuming you’re at the middle of the envelope (41 inches), it would have 65,600 inch-lbs of moment around the datum. Adding 2 pounds at the tailwheel (249 inches) adds 498 inch-pounds of moment. The total aircraft then weighs 1602 lbs with a moment of 66,098 inch-lbs. 66,098 / 1602 = 41.26 inches. The cg is moved aft by roughly a quarter of an inch. At gross weight, CG movement would be less than 0.20 inches. That's not insignificant, but tolerable, in my estimation.
Miles